Background: In order to elucidate the significance of myofibroblasts in invasive growth of colorectal adenocarcinomas, we examined the number of myofibroblasts at the tumor border of colorectal adenocarcinomas.
Method: A total of 91 invasive colorectal adenocarcinomas were examined immunohistochemically using anti-alpha-smooth muscle actin (ASMA) and high-molecular-weight caldesmon (h-CD) antibodies; 25 carcinomas confined to the submucosa (sm carcinomas), 40 carcinomas confined to the muscularis propria (mp carcinomas) and 26 carcinomas invading the subserosa or adventitia (ss carcinomas). We considered ASMA-positive and h-CD-negative stromal cells as myofibroblasts.
Results: Twenty-seven (67%) of the 40 mp carcinomas and 25 (96%) of the 26 ss carcinomas had a small number of myofibroblasts at the tumor border facing the muscularis propria.
Conclusions: Although direct evidence is lacking, there is a possibility that the further immediately vertical and radial invasion of carcinoma cells into the subserosa or adventitia is associated with a smaller number of myofibroblasts at the tumor border facing the muscularis propria in mp carcinomas, resulting in a low incidence of mp and a high incidence of ss carcinomas in the colorectum.